Organic light emitting display and method of driving the same

ABSTRACT

An organic light emitting display includes a mode determining unit adapted to determine whether the display is in a low power or common driving mode based on an operation control signal and to generate a control signal corresponding to the determined mode, a scan driver adapted to sequentially supply scan signals to scan lines, a data driver adapted to supply data signals to data lines in synchronization with the scan signals, pixels arranged at intersections of the scan lines and the data lines, and a timing controller adapted to control the scan driver and the data driver so that a frame frequency changes based on whether the low power driving mode or the common driving mode control signal is supplied from the mode determining unit, wherein the scan driver is adapted to uniformly maintain a pulse width of the scan signals regardless of a change in the frame frequency.

BACKGROUND

1. Field

Embodiments relate to an organic light emitting display and a method ofdriving the same. More particularly, embodiments relate to an organiclight emitting display and a method of driving such an organic lightemitting display capable of uniformly maintaining brightness and colorcoordinates so that a user cannot recognize a change in a framefrequency.

2. Description of the Related Art

Recently, various flat panel displays (FPD) that are lower in weight andsmaller in volume than comparable cathode ray tubes (CRT) have beendeveloped. FPDs generally include liquid crystal displays (LCD), fieldemission displays (FED), plasma display panels (PDP), and organic lightemitting displays.

Among the FPDs, organic light emitting displays may display images usingorganic light emitting diodes (OLED) that generate light by there-combination of electrons and holes. Organic light emitting displaysgenerally have characteristics such as relatively high response speedsand lower power consumption.

In general, organic light emitting displays include pixels arranged in amatrix. Each of the pixels may include at least two transistors and atleast one capacitor and organic light emitting diode (OLED).

The pixels may display an image with predetermined brightness byrespectively supplying currents corresponding to voltages charged in thecapacitors to the OLEDs via driving transistors. The capacitors may becharged with voltages corresponding to data signals, respectively,during a period when scan signals are supplied.

Organic light emitting displays may be adapted to be driving in a commondriving mode with a first frame frequency and a low-power driving modewith a second frame frequency that is lower than the first framefrequency. Organic light emitting displays that are adapted to maintainbrightness and/or color characteristics irrespective of changes in framefrequency are desired.

SUMMARY

Embodiments are therefore directed to organic light emitting displaysand methods of driving such organic light emitting displays, whichsubstantially overcome one or more of the problems due to thelimitations and disadvantages of the related art.

It is therefore a feature of an embodiment to provide an organic lightemitting display capable of uniformly maintaining brightness and colorcoordinates so that a user does not recognize a change in a framefrequency.

It is therefore a separate feature of an embodiment to provide a methodof driving an organic light emitting display capable of uniformlymaintaining brightness and color coordinates so that a user does notrecognize a change in a frame frequency.

It is therefore a separate feature of an embodiment to provide anorganic light emitting display that supplies scan signals having a samepulse width irrespective of a frame frequency and/or driving mode.

It is therefore a separate feature of an embodiment to provide a methodof driving an organic light emitting display that supplies scan signalshaving a same pulse width irrespective of a frame frequency and/ordriving mode.

At least one of the above and other features and advantages may berealized by providing an organic light emitting display, including amode determining unit adapted to determine whether the organic lightemitting display is in a low power driving mode or a common driving modebased on an operation control signal and to generate a control signalcorresponding to the determined mode, a scan driver adapted tosequentially supply scan signals to scan lines, a data driver adapted tosupply data signals to data lines in synchronization with the scansignals, pixels arranged at intersections of the scan lines and the datalines, and a timing controller adapted to control the scan driver andthe data driver so that a frame frequency changes based on whether thelow power driving mode or the common driving mode control signal issupplied from the mode determining unit, wherein the scan driver isadapted to uniformly maintain a pulse width of the scan signalsregardless of a change in the frame frequency.

The scan driver may be adapted to control a distance between apreviously supplied scan signal and a scan signal to be currentlysupplied based on the change in the frame frequency.

The mode determining unit may be adapted to supply a low power controlsignal corresponding to the low power driving mode to the timingcontroller when the operation control signal is not supplied during apredetermined period of time and to supply a common control signal tothe timing controller corresponding to the common driving mode at othertimes.

When the mode determining unit determines that the operation controlsignal has not been supplied during the predetermined period of time,the mode determining unit may additionally determine whether an imagecurrently displayed is a still image or a moving picture, and may beadapted to supply the low power control signal to the timing controlleronly when the image is determined as the still image.

The timing controller may be adapted to control the scan driver and thedata driver to be driven at a first frame frequency when the commondriving mode control signal is supplied and to be driven at a secondframe frequency when the low power driving mode control signal issupplied.

The first frame frequency may be higher than the second frame frequency.

The pixels may each include an organic light emitting diode (OLED), anda driving transistor adapted to control an amount of current supplied tothe OLED.

Each of the pixels may further include a plurality of transistors and astorage capacitor adapted to compensate for a threshold voltage of thedriving transistor.

At least one of the above and other features and advantages may beseparately realized by providing a method of driving an organic lightemitting display, including changing a frame frequency based on anexternally supplied operation control signal, uniformly maintaining apulse width of scan signals regardless of the frame frequency, andsupplying data signals in synchronization with the scan signals.

Uniformly maintaining the width of scan signals regardless of the framefrequency may include controlling a time period between scan pulses ofsubsequent ones of the scan signals based on the frame frequency.

The driving method may further include controlling emission andnon-emission states of emission control signals to be supplied toemission control lines based on the time periods between respective scanpulses.

Changing the frame frequency based on the externally supplied operationcontrol signal may include determining whether the organic lightemitting display is in a common driving mode or in a low power drivingmode based on the operation control signal, and setting the framefrequency as a first frame frequency for the common driving mode andsetting the frame frequency as a second frame frequency for the lowpower driving mode.

The first frame frequency may be higher than the second frame frequency.

Changing the frame frequency based on the externally supplied operationcontrol signal may include determining that the organic light emittingdisplay is in the low power mode when the operation control signal hasnot been input for a predetermined period of time.

Changing the frame frequency based on the externally supplied operationcontrol signal may include determining that the operation control signalhas not been input for a predetermined period of time, determiningwhether an image being displayed during the predetermined time is astill image or a moving picture, determining that the organic lightemitting display is in the low power mode when the image displayed isdetermined to be a still image and when the operation control signal hasnot been input during the predetermined period of time, and determiningthat the organic light emitting display is in the common driving modewhen the image displayed is determined to be a moving picture.

The method may further include generating light with predeterminedbrightness in pixels of the display based on the supplied data signals.

At least one of the above and other features and advantages may berealized by providing an organic light emitting display including aplurality of pixels, including a mode determining unit adapted todetermine whether the organic light emitting display is in a firstdriving mode corresponding to a first frame frequency or a seconddriving mode corresponding to a second frame frequency based on anoperation control signal and to generate a control signal correspondingto the determined mode, a scan driver; and a timing controller adaptedto control the scan driver so that a frame frequency changes based onwhether the display is in the first driving mode or the second drivingmode, wherein the scan driver is adapted sequentially supply scansignals having a same pulse width to scan lines during the first drivingmode and the second driving mode and a different, and wherein the scandriver is adapted to apply a first time period between the scan pulsesof consecutively driven scan lines during the first driving mode and toapply a second time period between the scan pulses of consecutivelydriven scan lines during the second driving mode, the first time periodbeing different from the second time period.

The first driving mode may be a common driving mode and the seconddriving mode may be a low power driving mode, and the first framefrequency may be faster than the second frame frequency.

The first time period may correspond to a time period between an endingedge of a (n−1)^(th) scan pulse and a beginning edge of an n^(th) scanpulse.

The scan driver may be further adapted to control emission andnon-emission states of emission control lines based on whether thedisplay is in the first driving mode or the second driving mode suchthat non-emission time of the emission control signals associated withthe first driving mode is different from the non-emission time of theemission control signals associated with the second driving mode by aninteger multiple of a difference in time between the first time periodand the second time period.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of ordinary skill in the art by describing in detail exemplaryembodiments with reference to the attached drawings, in which:

FIG. 1 illustrates a schematic diagram of an exemplary organic lightemitting display;

FIGS. 2A and 2B illustrate exemplary waveform diagrams of exemplary scansignals employable during a first driving mode having a first framefrequency and a second driving mode having a second frame frequency,respectively, for maintaining brightness and/or color characteristics ofpixels being driven;

FIG. 3 illustrates a schematic diagram of an exemplary embodiment of apixel structure employable with the display FIG. 1; and

FIG. 4 illustrates an exemplary waveform diagram of signals employableby an exemplary embodiment of a method of driving a pixel.

DETAILED DESCRIPTION

Korean Patent Application No. 10-2009-0083930, filed on Sep. 7, 2009, inthe Korean Intellectual Property Office, and entitled: “Organic LightEmitting Display and Driving Method Thereof” is incorporated byreference herein in its entirety.

Exemplary embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, aspects may be embodiedin different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the following description, it will be understood that when a firstelement is described as being coupled to a second element, the firstelement may be directly coupled to the second element but may also beindirectly coupled to the second element via one or more other elements.Further, some of the elements that are not essential to the completeunderstanding of the invention are omitted for clarity. Also, likereference numerals refer to like elements throughout the specification.

FIG. 1 illustrates a schematic diagram of an exemplary organic lightemitting display 100.

Referring to FIG. 1, the organic light emitting display 100 may includea pixel unit 130, including pixels 140 coupled to scan lines S1 to Snand data lines D1 to Dm, a scan driver 110 for driving the scan lines S1to Sn and emission control lines E1 to En, a data driver 120 for drivingthe data lines D1 to Dm, a timing controller 150 for controlling thescan driver 110 and the data driver 120, and a mode determining unit 160for determining a driving mode.

The mode determining unit 160 may determine a driving mode based on anexternally supplied operation control signal and may supply a controlsignal corresponding to the determined driving mode to the timingcontroller 150. The operation control signal may be, e.g., a signalinput to a key board, movement of a mouse, etc.). Driving modes mayinclude, e.g., a common driving mode, a low-power driving mode, etc. Themode determining unit 160 may also receive external data Data. The modedetermining unit 160 may determine an image to be displayed by the pixelunit 130 and may determine the driving mode corresponding to thedetermined image.

For example, the mode determining unit 160 may determine that thedisplay 100 is to be driven in a low power driving mode when anoperation control signal, e.g., a signal input by a keyboard, has notbeen input during a predetermined period of time and may supply a lowpower control signal to the timing controller 150. Further, e.g., themode determining unit 160 may determine that the display 100 is to bedriven in a common driving mode when an operation control signal, e.g.,has been input during the predetermined period of time, and may supply acommon control signal to the timing controller 150.

More particularly, e.g., when an operation control signal has not beeninput during the predetermined period, the mode determining unit 160 maydetermine the image to be displayed by the pixel unit 130 based onexternally supplied data Data. In some cases, e.g., when an operationcontrol signal has not been input during the predetermined period, theimage to be displayed may be a still image. In such cases, e.g., whenthe determined image is a still image, and it is determined that anoperation control signal has not been input during the predeterminedperiod, the mode determining unit 160 may supply the low power controlsignal to the timing controller 150. On the other hand, in someembodiments, if the mode determining unit 160 determines that thecurrent image to be displayed is a moving picture, the mode determiningunit 160 may supply the common control signal to the timing controller150 even when it is determined that the operation control signal has notbeen input during the predetermined time.

The predetermined period of time during which it may determined whetheran operation control signal has/has not been input, may be set based,e.g., on user preferences, default settings, etc. That is, embodimentsare not limited to specific predetermined periods of time. For example,the predetermined period of time may be experimentally determined basedon an environment in which a monitor is to be provided.

The timing controller 150 may generate data driving control signals DCSand scan driving control signals SCS based on externally suppliedsynchronizing signals/data Data. The data driving control signals DCSmay be supplied to the data driver 120 and the scan driving controlsignals SCS may be supplied to the scan driver 110. The timingcontroller 150 may supply the externally supplied data Data to the datadriver 120.

The timing controller 150 may supply a first frame control signal to thescan driver 110 and the data driver 120 when the common control signalis input. The timing controller 150 may supply a second frame controlsignal to the scan driver 110 and the data driver 120 when the low powercontrol signal is input. The first frame control signal and the secondframe control signal are included in the scan driving control signal SCSand the data driving control signal DCS.

The scan driver 110 may receive the scan driving control signals SCSfrom the timing controller 150. After receiving the scan driving controlsignals SCS, the scan driver 110 may generate scan signals and maysequentially supply the generated scan signals to the scan lines S1 toSn. In addition, the scan driver 110 may generate emission controlsignals in response to the scan driving control signals SCS. The scandriver 110 may sequentially supply the generated emission controlsignals to the emission control lines E1 to En. A width of the emissioncontrol signals may be equal to or larger than a width of the scansignals.

The scan driver 110 may control a distance or time period between scanpulses of sequentially applied ones the generated scan signals based onwhether the first frame control signal or the second frame controlsignal was supplied to the scan driver 110. FIGS. 2A and 2B illustrateexemplary waveform diagrams of exemplary scan signals employable duringa first driving mode having a first frame frequency, and a seconddriving mode having a second frame frequency, respectively. Moreparticularly, FIG. 2A illustrates exemplary scan signals that may besupplied according to the first frame frequency, e.g., corresponding tothe common driving mode when the common control signal may have beensupplied to the scan driver 110, and FIG. 2B illustrates exemplary scansignals that may be supplied according to the second frame frequency,e.g., corresponding to a lower frequency of the low power driving modewhen the low power control signal may have been supplied to the scandriver 110. For example, the first frame frequency during the commondriving mode may be 60 Hz and the second frame frequency during the lowpower driving mode may be 40 Hz.

Referring to FIG. 2A, according to the first frame frequency, e.g., thescan driver 110 may respectively supply scan signals including pulsesaccording to a first time period T1 to the scan lines S1 to Sn and adistance between an end of the scan pulse of scan signal of the(n−1)^(th) scan line Sn−1 and a start of the scan pulse of the scansignal of the n^(th) scan line Sn may correspond to a second time periodT2. Referring to FIG. 2B, according to the second frame frequency, e.g.,the scan driver may respectively supply scan signals including pulsesaccording to the first time period T1 to the scan lines S1 to Sn and adistance between an end of the scan pulse of the scan signal of the(n−1)^(th) scan line Sn−1 and a start of the scan pulse of the scansignal of the nth scan line Sn may correspond to a third time period T3.

As shown in FIGS. 2A and 2B, widths of the scan pulses may correspond tothe first time period T1 irrespective of whether the first frame controlsignal or the second frame control signal was supplied to the scandriver 110. Thus, e.g., during the common driving mode and the low powerdriving mode, widths of the scan pulses of the respective scan signalsapplied to the scan lines S1-Sn may be the same. On the other hand,based on whether the first frame control signal or the second framecontrol signal was supplied to the scan driver 110, e.g., whether thepixel unit 130 is to be driven under the common driving mode or the lowpower driving mode, time periods between scan pulses of subsequent onesof the scan signals, e.g., the (n−1)^(th) and n^(th) scan signals, maybe controlled to correspond to the second time period T2 for the firstframe frequency and to correspond to the third time period T3 for thesecond frame frequency. In such embodiments, the second time period T2may be different from, e.g., shorter than, the third time period T3.That is, e.g., in the low power mode, more time may elapse between scanpulses of subsequent ones of the scan signals in accordance with aslower frame frequency.

The scan driver 110 may control on/off times of the emission controlsignals based on the scan signals. More particularly, the scan driver110 may control emission/non-emission time periods of the emissioncontrol signals based on the frame frequency. For example, withreference to FIG. 2A, in the exemplary case of two scan signals beingsupplied to the (n−1)^(th) and n^(th) scan lines S(n−1) and Sn, the scandriver 110 may controllably supply emission control signals that mayoverlap the first time period T1 of the scan pulse supplied to(n−1)^(th) scan line S(n−1), the first time period T1 of the scan pulsesupplied to the n^(th) scan signal Sn, and the second time period T2corresponding to the time between the respective pulses being drivenaccording to the first frame frequency. Further, with reference to FIG.2B, e.g., in the exemplary case of two scan signals being supplied tothe (n−1)^(th) and n^(th) scan lines S(n−1) and Sn, the scan driver 110may controllably supply emission control signals that may overlap thefirst time period T1 of the scan pulse supplied to (n−1)^(th) scan lineS(n−1), the first time period T1 of the scan pulse supplied to then^(th) scan signal Sn, and the third time period T3 corresponding to thetime between the respective pulses being driven according to the secondframe frequency. More particularly, referring to FIGS. 2A and 2B, theemission control signals supplied to the n^(th) emission control line Enmay be “high” or in a “non-emission state” while the respective scanpulses are supplied to the (n−1)^(th) and the n^(th) scan lines S(n−1)and Sn as well as the second time period T2 (shown in FIG. 2Acorresponding to the first frame frequency) or the third time period T3(shown in FIG. 2B corresponding to the second frame frequency) lapsingbetween the two subsequent scan signals.

The scan driver 110 may supply scan signals including scan pulses havinga first width corresponding to the first time period T1 regardless of achange in frame frequency. Accordingly, embodiments may enable storagecapacitors included in pixels, e.g., the pixels 140 of FIG. 1, to have auniform charge period irrespective of a change in frame frequency.Embodiments may be advantageous by enabling brightness and/or colorcharacteristics of pixels to be desensitized at least to changes inframe frequency. That is, e.g., embodiments may enable brightness and/orcolor characteristics of pixels to be uniformly maintained at leastirrespectively of changes in frame frequency.

The data driver 120 may receive the data driving control signals DCSfrom the timing controller 150. After receiving the data driving controlsignals DCS, the data driver 120 may generate data signals and supplythe generated data signals to the data lines D1 to Dm in synchronizationwith the scan signals.

The pixel unit 130 may receive a voltage of a first external powersource ELVDD and a voltage of a second external power source ELVSS andmay supply the received first and second power source ELVDD and ELVSSvoltages to the pixels 140. Using the received first and second powersource ELVDD and ELVSS voltages, the pixels 140 may generate lightcomponents corresponding to the data signals. More particularly, e.g.,the pixels 140 positioned along an i^(th) (i is a natural number)horizontal line of a matrix pattern may initialize gate electrodes ofdriving transistors during a period where a respective scan signal issupplied to the (i−1)^(th) scan line S(i−1) and may charge voltagescorresponding to the data signals and the threshold voltages of thedriving transistors during a period where the scan signal is supplied tothe i^(th) scan line Si.

As described above, embodiments may enable various types of pixelstructures, e.g., pixel structures including a storage capacitor, allpixel structures that charge a voltages corresponding to respective datasignals when respective scan signals are supplied, etc., to bedesensitized at least to changes in frame frequency. That is, asdescribed above, embodiments may enable various types of pixelsstructures, e.g., pixel structures including a storage capacitor, allpixel structures that charge a voltages corresponding to respective datasignals when respective scan signals are supplied, etc., to uniformlymaintain brightness and/or color characteristics thereof irrespectivelyof changes in frame frequency by maintaining a charge time of thestorage capacitor associated therewith.

FIG. 3 illustrates a schematic diagram of an exemplary embodiment of apixel 140 nm employable with the display 100 FIG. 1 and with which oneor more features described herein may be applied. It is understood bypersons of ordinary skill in the art that the pixel structure of thepixels 140 nm may be adapted to compensate for a threshold voltage of adriving transistor of the pixel.

For description purposes, the exemplary pixels 140 nm illustrated inFIG. 3 is coupled to the m^(th) data line Dm, the nth scan line Sn, the(n−1)th scan line Sn−1, and the nth emission control line En.Embodiments are not limited thereto. For example, the pixel 140 nm ofFIG. 3 may be used as one, some or all of the pixels 140 of the display100 of FIG. 1.

Referring to FIG. 3, the pixel 140 nm may include a pixel circuit 142coupled to an OLED, the data line Dm, the scan lines Sn−1 and Sn, andthe emission control line En. The pixel circuit 142 may control anamount of current supplied to the OLED.

An anode electrode of the OLED may be coupled to the pixel circuit 142and a cathode electrode of the OLED may be coupled to the second powersource ELVSS. A voltage value of the second power source ELVSS may beset to be lower than a voltage value of the first power source ELVDD.The OLED may generate light with predetermined brightness correspondingto an amount of current supplied from the pixel circuit 142.

The pixel circuit 142 may control the amount of current supplied to theOLED corresponding to the data signal supplied to the data line Dm whenthe scan signal is supplied to the scan line Sn. More particularly,e.g., the pixel circuit 142 may includes first to sixth transistors M1to M6 and a storage capacitor Cst.

A first electrode of the second transistor M2 may be coupled to the dataline Dm and the second electrode of the second transistor M2 may becoupled to a first node N1. A gate electrode of the second transistor M2may be coupled to the n^(th) scan line Sn. The second transistor M2 maybe turned on when the scan signal is supplied to the n^(th) scan line Snand, when the second transistor M2 is turned on, it may enable the datasignal supplied to the data line Dm to be supplied the first node N1.

A first electrode of the first transistor M1 may be coupled to the firstnode N1 and a second electrode of the first transistor M1 may be coupledto the first electrode of the sixth transistor M6. A gate electrode ofthe first transistor M1 may be coupled to a first terminal of thestorage capacitor Cst. The first transistor M1 may supply a currentcorresponding to a voltage charged in the storage capacitor Cst to theOLED.

A first electrode of the third transistor M3 may be coupled to thesecond electrode of the first transistor M1 and a second electrode ofthe third transistor M3 may be coupled to the gate electrode of thefirst transistor M1. A gate electrode of the third transistor M3 may becoupled to the nth scan line Sn. The third transistor M3 may be turnedon when the scan signal is supplied to the nth scan line Sn, and, whenthe third transistor M3 is turned on, may cause the first transistor M1to be in a diode-connected state.

A gate electrode of the fourth transistor M4 may be coupled to the(n−1)th scan line Sn−1 and a first electrode of the fourth transistor M4may coupled to the first terminal of the storage capacitor Cst and thegate electrode of the first transistor M1. A second electrode of thefourth transistor M4 may be coupled to an initialization power sourceVint. The fourth transistor M4 may be turned on when the scan signal issupplied to the (n−1)^(th) scan line Sn−1 and, when the fourthtransistor M4 is turned on, a voltage of the first terminal of thestorage capacitor Cst and the gate electrode of the first transistor M1may change corresponding to the voltage of the initialization powersource Vint.

A first electrode of the fifth transistor M5 may be coupled to the firstpower source ELVDD and the second electrode of the fifth transistor M5may be coupled to the first node N1. A gate electrode of the fifthtransistor M5 may be coupled to the emission control line En. The fifthtransistor M5 may be turned on when the emission control signal is notsupplied, e.g., in a non-emission state, from the emission control lineEn so that the first power source ELVDD may be electrically coupled tothe first node N1.

A first electrode of the sixth transistor M6 may be coupled to thesecond electrode of the first transistor M1 and a second electrode ofthe sixth transistor M6 may be coupled to the anode electrode of theOLED. A gate electrode of the sixth transistor M6 may be coupled to theemission control line En. The sixth transistor M6 may be turned on whenthe emission control signal is not supplied, e.g., non-emission state,to supply the current supplied from the first transistor M1 to the OLED.

FIG. 4 illustrates an exemplary waveform diagram of signals employableby an exemplary embodiment of a method of driving the pixel 140 nm ofFIG. 3.

Referring to FIGS. 3 and 4, first, the scan signal may be supplied tothe (n−1)^(th) scan line Sn−1 so that the fourth transistor M4 may beturned on. When the fourth transistor M4 is turned on, a voltage of theinitialization power source Vint may be supplied to the first terminalof the storage capacitor Cst and the gate terminal of the firsttransistor M1. That is, when the fourth transistor M4 is turned on, thevoltages at the first terminal of the storage capacitor C and the gateterminal of the first transistor M1 may be initialized to the voltage ofthe initialization power source Vint. The voltage value of theinitialization power source Vint may be set to be smaller than thevoltage value of the data signal.

Then, the scan signal may be supplied to the n^(th) scan line Sn. Whenthe scan signal is supplied to the n^(th) scan line Sn, the secondtransistor M2 and the third transistor M3 may be turned on. When thethird transistor M3 is turned on, the first transistor M1 may be coupledin the form of a diode. When the second transistor M2 is turned on, thedata signal supplied to the data line Dm may be supplied to the firstnode N1 via the second transistor M2. At this time, because the voltageof the gate terminal of first transistor M1 may be set at the voltage ofthe initialization power source Vint (that is, set to be smaller thanthe voltage of the data signal supplied to the first node N1), the firsttransistor M1 may be turned on.

When the first transistor M1 is turned on, the data signal applied tothe first node N1 may be supplied to the first terminal of the storagecapacitor Cst via the first transistor M1 and the third transistor M3.Since the data signal is supplied to the storage capacitor Cst via thefirst transistor M1 in the diode-connected state, the data signal andthe voltage corresponding to the threshold voltage of the firsttransistor M1 may be charged in the storage capacitor Cst.

After the voltages corresponding to the data signal and the thresholdvoltage of the first transistor M1 are charged in the storage capacitorCst, the emission control signals EMI may be changed from a non-emissionstate, e.g., high level, to an emission state, e.g., low level, so thatthe fifth transistor M5 and the sixth transistor M6 may be turned on.When the fifth transistor M5 and the sixth transistor M6 are turned on,a current path from the first power source ELVDD to the OLED is formed.In this case, the first transistor M1 may control an amount of currentthat flows from the first power source ELVDD to the OLED correspondingto the voltage charged in the storage capacitor Cst.

Here, since the voltage corresponding to the threshold voltage of thefirst transistor M1 as well as the data signal may be additionallycharged in the storage capacitor Cst included in the pixel 140, anamount of current that flows to the OLED may be controlled regardless ofthe threshold voltage of the first transistor M1.

More importantly, in the driving waveforms of FIG. 4, for driving of thepixel 140 nm according to any frame frequency, e.g., a first framefrequency, second frame frequency, etc., only a time period T4 betweenscan pulses of subsequent scan signals, e.g., scan signals applied tothe (n−1)^(th) and the n^(th) scan lines S(n−1), may be changed based ona frame frequency of a current driving mode. That is, in embodiments,irrespective of a frame frequency of a current driving mode, a timeperiod T1 corresponding to a pulse width of respective scan signals mayremain constant. More particularly, in embodiments, irrespective of aframe frequency of a current driving mode, a charge time of a storagecapacitor Cst may remain constant. Referring to TABLE 1, an effect onbrightness corresponding to a change in a width of a scan pulse of ascan signal, as applied to the pixel 140 nm of FIG. 3.

TABLE 1 Frame Frequency 60 Hz 40 Hz 60 Hz Width (μs) of Scan Signal 2639 26 Brightness (cd/m²) 560 525 561

Referring to TABLE 1, when the width of the scan pulse corresponding tothe time T1 is changed, i.e., not maintained as constant, based on arespective frame frequency, the brightness changes. More particularly,when the width of the scan pulse is changed from 26 μs for a framefrequency of 60 Hz to 39 μs for a frame frequency of 40 Hz, thebrightness changes from about 560 cd/m² to about 525 cd/m². Thus, insuch cases, a charge time of the storage capacitor changes correspondingto the change in the pulse width of the scan signals such that thebrightness changes.

As described above, however, embodiments may be advantageous byproviding an organic light emitting display and/or a driving method fordriving an organic light emitting display that may maintain a timeperiod of scan pulses at a predetermined constant irrespective of aframe frequency and/or driving mode. Embodiments may separately enable acharge time of a storage capacitor of a pixel to be maintained constantirrespective of a frame frequency and/or driving mode. Embodiments mayseparately enable brightness and/or color characteristics of pixels tobe desensitized to changes in frame frequency and/or driving modes,e.g., brightness and/or color characteristics may be uniformlymaintained irrespective of frame frequency.

Exemplary embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

What is claimed is:
 1. An organic light emitting display, comprising: amode determining unit adapted to determine whether the organic lightemitting display is in a low power driving mode or a common driving modebased on an operation control signal and to generate a control signalcorresponding to the determined mode; a scan driver adapted tosequentially supply scan signals to scan lines; a data driver adapted tosupply data signals to data lines in synchronization with the scansignals; pixels arranged at intersections of the scan lines and the datalines; and a timing controller adapted to control the scan driver andthe data driver so that a frame frequency changes based on whether thelow power driving mode or the common driving mode control signal issupplied from the mode determining unit, wherein the scan driver isadapted to uniformly maintain a pulse width of the scan signalsregardless of a change in the frame frequency.
 2. The organic lightemitting display as claimed in claim 1, wherein the scan driver isadapted to control a distance between a previously supplied scan signaland a scan signal to be currently supplied based on the change in theframe frequency.
 3. The organic light emitting display as claimed inclaim 1, wherein the mode determining unit is adapted to supply a lowpower control signal corresponding to the low power driving mode to thetiming controller when the operation control signal is not suppliedduring a predetermined period of time and to supply a common controlsignal to the timing controller corresponding to the common driving modeat other times.
 4. The organic light emitting display as claimed inclaim 3, wherein, when the mode determining unit determines that theoperation control signal has not been supplied during the predeterminedperiod of time, the mode determining unit additionally determineswhether an image currently displayed is a still image or a movingpicture, and is adapted to supply the low power control signal to thetiming controller only when the image is determined as the still image.5. The organic light emitting display as claimed in claim 1, wherein thetiming controller is adapted to control the scan driver and the datadriver to be driven at a first frame frequency when the common drivingmode control signal is supplied and to be driven at a second framefrequency when the low power driving mode control signal is supplied. 6.The organic light emitting display as claimed in claim 5, wherein thefirst frame frequency is higher than the second frame frequency.
 7. Theorganic light emitting display as claimed in claim 1, wherein each ofthe pixels comprises: an organic light emitting diode (OLED); and adriving transistor adapted to control an amount of current supplied tothe OLED.
 8. The organic light emitting display as claimed in claim 7,wherein each of the pixels further comprises a plurality of transistorsand a storage capacitor adapted to compensate for a threshold voltage ofthe driving transistor.
 9. A method of driving an organic light emittingdisplay, comprising: changing a frame frequency based on an externallysupplied operation control signal; uniformly maintaining a pulse widthof scan signals regardless of the frame frequency; and supplying datasignals in synchronization with the scan signals.
 10. The method asclaimed in claim 9, wherein uniformly maintaining the width of scansignals regardless of the frame frequency includes controlling a timeperiod between scan pulses of subsequent ones of the scan signals basedon the frame frequency.
 11. The method as claimed in claim 10, furthercomprising: controlling emission and non-emission states of emissioncontrol signals to be supplied to emission control lines based on thetime periods between respective scan pulses.
 12. The method as claimedin claim 9, wherein changing the frame frequency based on the externallysupplied operation control signal includes: determining whether theorganic light emitting display is in a common driving mode or in a lowpower driving mode based on the operation control signal; and settingthe frame frequency as a first frame frequency for the common drivingmode and setting the frame frequency as a second frame frequency for thelow power driving mode.
 13. The method as claimed in claim 12, whereinthe first frame frequency is higher than the second frame frequency. 14.The method as claimed in claim 12, wherein changing the frame frequencybased on the externally supplied operation control signal includes:determining that the organic light emitting display is in the low powermode when the operation control signal has not been input for apredetermined period of time.
 15. The method as claimed in claim 12,changing the frame frequency based on the externally supplied operationcontrol signal includes: determining that the operation control signalhas not been input for a predetermined period of time, determiningwhether an image being displayed during the predetermined time is astill image or a moving picture, determining that the organic lightemitting display is in the low power mode when the image displayed isdetermined to be a still image and when the operation control signal hasnot been input during the predetermined period of time, and determiningthat the organic light emitting display is in the common driving modewhen the image displayed is determined to be a moving picture.
 16. Themethod as claimed in claim 9, further comprising generating light withpredetermined brightness in pixels of the display based on the supplieddata signals.